Microstrip junction circulator wherein the ferrite body is disposed on the dielectric slab



Sept. 16, 1969 v. E. DUNN ET AL 3,467,918

MICROSTRIP JUNCTION CIRCULATOR WHEREIN THE FERRITE BODY IS DISPOSED ONTHE DIELECTRIC SLAB Filed Dec 21, 1967 3 Sheets-Sheet 1 r n f J J(PR/0f? ART) FERROMAGNET/C '6 L .075

HW (PR/0!? ART} INVENTORS VERNON E. DUNN BY ANTHONY J. DOMENICO #M, ML WATTORNEYS Sept. 16. 1969 v. E. DUNN T A MICROSTRIP JUNCTION CIRCULATORWHEREIN THE FERRITE BODY 15 DISPOSED ON THE DIELECTRIC SLAB 5Sheets-Sheet 2 Filed Dec. 21, 1967 F/G. a

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N 4 N NW 0 mm N I T mw T D. YA EJ VI NN O O I NH 2M VA 1 Sept. 16, 1969v. E. DUNN ETAL 3,467,918

MICROSTRIP JUNCTION CIRCULATOR WHEREIN THE FERRITE BODY 15 DISPOSED ONTHE DIELECTRIC SLAB Filed Dec. 21, 1967 S'SheetS-Sheet z 6| 00 F/G. /364 320 250 24c 64 e4-fuj MP -2|u -zzo F/G. /4

68 67 \24b ,66 [23b ZIV" 7 l F/G. /5 as INVENTORS VERNON Ev DUNN 69 66ANTHONY J. DOMENICO 1M, M9 4 F/G. 6 M m ATTORNEYS United States PatentUS. Cl. 333-11 7 Claims ABSTRACT OF THE DISCLOSURE A circulator for usewith microstrip transmission lines in which ferromagnetic material isdisposed above and coupled to microstrip transmission lines and a DCmagnetic field is applied in a direction which is perpendicular thereto.

BACKGROUND OF THE INVENTION This invention relates generally to acirculator and more particularly to a circulator employing microstriptransmission lines.

A microstrip transmission line generally comprises a ground plane and aconductor (usually rectangular in cross-section) mounted in spacedrelationship with respect thereto. Usually, the conductor is carried ona dielectric slab which is carried on the ground plane and which servesto maintain the spacing. The dimensions of the conductor are selected togive desired impedance characteristics to the transmission line. Thedielectric used may be any one of a number of dielectric materials knownin the art, such as beryllia, polystyrene or alumina.

This type of transmission line permits making intricate microwavecircuits by conventional masking and etching techniques.

In microstrip circulators of the prior art a hole is drilled in thedielectric slab and ferromagnetic material placed in the hole. Theconductors are then formed over the ferrite and dielectric material toform a circulator junction. The ends of the conductors are adapted to beconnected to associated transmission lines.

Disadvantages of this type of circulator are that the dielectric isdifficult and expensive to machine, the device is large, and because ofthe different dielectric constants involved, impedance matching is poor.

SUMMARY OF THE INVENTION AND OBJECTS The present invention provides amicrostrip circulator in which the ferromagnetic material carries aconducting circuit on one surface thereof and is placed with its othersurface on a microstrip transmission line having conductors extendingtowardsa common region. Means are provided to couple the ferromagneticcircuit to the transmission line conductors. A perpendicular D-Cmagnetic field is applied across the device.

It is an object of this invention to provide a simple, inexpensive andeasily manufactured microstrip circulator.

It is another object of the present invention to provide a microstripcirculator which can be easily tuned to provide optimum operation atdesired center frequencies.

It is another object of the present invention to pro- ICC vide acirculator for microstrip geometry that does not require drilling a holein the dielectric.

These and other objects of the invention will become more apparent inconnection with the following description and drawings.

Brief description of the drawing FIGURE 1 is a perspective view of aprior art microstrip transmission line.

FIGURE 2 is a sectional view taken along line 22 of FIGURE 1.

FIGURE 3 is a perspective view of a microstrip circulator in accordancewith the present invention.

FIGURE 4 is a plan view of the microstrip portion of the circulator ofFIGURE 3.

FIGURE 5 is a plan view of the ferromagnetic portion of the circulatorof FIGURE 3.

FIGURE 6 is a side elevational view of the circulator shown in FIGURE 3together with a magnet for providing the D-C magnetic biasing field.

FIGURE 7 is the equivalent circuit of the circulator shown in FIGURES3-6.

FIGURE 8 is a plan view of 'a circulator showing one means for tuning.

FIGURES 9 and 10 are side elevational and plan views of anotherferromagnetic assembly for use in the invention.

FIGURE 11 is a perspective view of a circulator incorporating aferromagnetic assembly of the type shown in FIGURES 9 and 10.

FIGURE 12 is the equivalent circuit for the circulator of FIGURE 11.

FIGURE 13 shows a circulator having the D-C magnetic field provided byan electromagnet.

FIGURE 14 shows another circulator in accordance with the invention.

FIGURES 15 and 16 show a circulator including means for improving thecapacitive coupling between the ferromagnetic circuit and the microstriptransmission lines.

Description of the preferred embodiments A typical microstriptransmission line geometry is illustrated in FIGURES l and 2. Themicrostrip transmis sion line comprises a slab or water of dielectricmaterial 11 such as polystyrene, beryllia or alumina. This dielectricslab is plated or coated on one side with a metal film 12 which formsthe ground plane for the transmission line. One or more conductors arecarried by the other surface of the slab. One conductor 13 is shown. Thedimensions of the conductor 13 determine the characteristic impedance ofthe transmission line formed by the conductor, dielectric slab andground plane.

FIGURE 2 shows the electric and magnetic fields 14 and 16, respectively,associated with a microwave signal propagating on the microstriptransmission line. It is noted that the higher the dielectric constantof the dielectric material, the greater is the concentration of energyin the dielectric material.

In general, microstrip transmission lines may be formed by coating orplating both surfaces of a slab or wafer 11 with metallic material suchas copper, silver or gold. One surface is then masked, such as by silkscreen or photographic techniques, and subsequently etched to remove theunprotected metal and leave the desired conductive pattern on thesurface. By this means, relatively complex microwave circuits can beformed. Techniques 3 of this type are well known in the electronic art,particularly in the printed circuit, microcircuit and integrated circuitart.

A circulator in accordance with the present invention is illustrated inFIGURES 3-6. The circulator comprises a slab of dielectric material 21including a ground plane 22. Three transmission lines are defined by theconverging conductors 23, 24 and 25 carried on the other surface of theslab 21. Each of the transmission lines defined by the conductors 23-25,dielectric 21 and ground plane 22 ends in an open circuit in the region30. This is more clearly illustrated in FIGURE 4. The ends of theconductors 23, 24 and 25 may be enlarged as shown at 27, 28 and 29,respectively. This increases the capacitance between the conductors andthe ground plane. The conductors and enlarged areas may be formed bymasking and etching as described above.

A disc 31 of ferromagnetic material, such as ferrite oryttrium-iron-garnet, is disposed over the region 30 above each of theenlarged areas 27, 28 and 29. The top surface of the ferromagneticmaterial carries a conductive circuit 32. In this particular instance,the circuit includes arms 33, 34 and 35 which join at the center of thedisc 31 and extend radially outwardly to the edge. Enlarged areas 37, 38and 39 are formed at the ends of the arms 33, 34 and 35, respectively.The areas 37, 38 and 39 capacitively couple to the enlarged areas 27, 28and 29, whereby the ferrite circuit 32 is electrically coupled to theconductors 23, 24 and 25. The circuit 32 is coupled to the ground sideof the transmission line 22 through the ferromagnetic material 31 anddielectric material 21 to form transmission lines. The dimensions of theconductive pattern 32 formed on the surface of the ferromagneticmaterial can be selected whereby there is an impedance match between thetransmission line circuit including conductor 32 and the convergingtransmission lines including conductors 23, 24 and 25.

A D-C magnetic field 41 is applied perpendicular to the plane of theferromagnetic disc. This can be applied by a permanent magnet or by anelectromagnet. Referring particularly to FIGURE 6, there is shown apermanent magnet 42 disposed on the ferromagnetic disc and having northand south poles as indicated. An insulating dielectric 43 is sandwichedbetween the magnet and ferrite disc so that the circuit 32 is notelectrically shorted.

The circulator provides a circulator action in accordance with wellknown theory. Referring particularly to FIGURE 3 and with the magneticfield indicated: energy indicated at port 43 will emerge from port 44;energy incident at port 44 will emerge from port 45; and energy incidentat port 45 will emerge from port 43. As previously described, theimpedance and capacitance of the various areas are selected to give thedesired frequency response and circulator characteristics.

An equivalent circuit for the circulator illustrated in FIGURES 3-6 isshown in FIGURE 7. The ferrite material is regarded as a non-reciprocalinductance and is illustrated by the inductors 51, 52 and 53, and arrow54. The capacitance formed between the pads or enlarged areas 27, 28 and29 and ground is indicated by the capacitors 27a, 28a and 29a. Thecoupling capacitance between the transmission line portions 27, 28 and29 and the enlarged portions 37, 38 and 39 of the ferrite circuit 32 isindicated by the capacitors 37a, 38a and 39a. Explanation of theoperation of circulators of this type is described fully in US. PatentNo. 3,286,201.

A microstrip circulator in accordance with the foregoing was constructedto operate at 1900 mHz. The ferromagnetic material was ferritecomprising aluminum doped yttrium-iron garnet with a saturationmagnetization of 300 gauss having a diameter of .80 inch and thicknessof .10 inch. The dimensions of the circuit 32 are shown in FIGURE 5. Themicrostrip transmission line was constructed of alumina dielectric .060inch thick with the width of the transmission lines 23, 24 and 25 being.070 inch. In operation, the circulator had a bandwidth of 50 mHz. witha center frequency of 1900 mHz. The insertion loss was 1.6 db andisolation between ports was 20 db.

In certain instances it may be desirable to adjust the capacitances 37a,38a, 39a to tune the circulator. This may be achieved by rotating theferrite disc through an angle 0 as shown in FIGURE 8. Thus, the enlargedareas 27, 28 and 29 and 37, 38 and 39 are displaced with respect to oneanother to thereby decrease the coupling capacity.

In FIGURES 9, 10 and 11, there is shown a terminated circulator orisolator which includes a shunting resistance in parallel with one ofthe coupling capacitors between the ferrite transmission line and themicrostrip transmission line. FIGURE 9 shows a view of the bottom offerrite disc 3111. A conductive pad or area 56 is formed at one port. Aresistive film 57 is formed on the edge of the disc, FIGURE 10, andresistively connects the area 56 with the arms of circuit 32. FIGURE 11is a perspective view showing an assembled circulator.

FIGURE 12 is the equivalent circuit for the circulator shown in FIGURE11. It is observed that the equivalent circuit is identical to thatshown in FIGURE 7 with the exception that resistor 57 is in shunt withthe coupling capacitor 38a.

In FIGURE 13, there is shown a circulator in which the field is appliedby an electromagnet 61 including coil 62. The circulator may be switchedresponsive to a change in current. Alternately, the coil material may bechosen to have a high remanent field and in this case the circulator maybe made to switch with latching action by application of a currentpulse.

FIGURE 14 shows a circulator including a slab 21a, ground plane 22a anda ferromagnetic disc 31a having circuit 32a over the convergingconductors 23a, 24a and 25a. The area between the ends of conductors23a, 24a, 25a is larger than the ferromagnetic material 31 whereby whenthe ferrite is placed on the dielectric slab 21a, it rests directly onthe slab. Electrical connection is made between the circuit 32a and theconductors 23a, 24a and 25a by means of tabs 64 by soldering, welding orotherwise attaching.

FIGURES 15 and 16 illustrate a means for achieving better capacitivecoupling between the ferrite circuit and the microstrip transmissionline circuit. In this instance, a dielectric ring 66 is formed about theferrite disc 67. The conductive pattern 68 is then formed on the topsurface in the manner previously described. The coupling between thecircuit 68 and conductors 23b, 24b and 25b is through the higherdielectric ring and capacitive coupling can be controlled by properchoice of dielectric constant of the ring.

Although the invention has been described and illustrated with referenceto specific embodiments, other embodiments will be apparent to personsskilled in the art. The invention is, therefore, only to be limited bythe scope of the following claims.

We claim:

1. A circulator comprising at least three transmission lines convergingtowards a common region, said transmission lines including a commonground plane and at least three conductors, a slab of dielectricmaterial carried on one surface of said ground plane and said at leastthree conductors carried on the opposite surface of said slab and havingends converging towards said region with the ends spaced from oneanother, a ferrite body disposed with one surface on said oppositesurface of said slab at said region, a conductive pattern carried on theopposite surface of said ferrite body, means for coupling saidconductive pattern on the ferrite body to the ends of said conductors,and means for applying a DC magnetic field substantially perpendicularto said ferrite material.

2. A circulator as in claim 1 wherein said coupling means comprisesenlarged portions formed at the ends of said conductors and enlargedportions formed on the conductive pattern, said portions being disposedopposite one another.

3. A circulator as in claim 2 wherein said ferrite body may be rotatedto adjust the coupling between said enlarged portions.

4. A circulator as in claim 2 wherein said ferrite body includes a ringhaving a dilferent dielectric constant in the regions of said enlargedportions to thereby increase or decrease the capacitive coupling betweenthe ends of the conductors and the conductive pattern.

5. A circulator as in claim 1 terminated at one point by a resistivefilm connected between the end of each of the conductors and theconductive pattern.

6. A circulator as in claim 1 wherein the ends of the Hershenov: X-BandMicrostrip Circulator, Proc. of the IEEE, December 1966, pp. 2022, 2023cited.

HERMAN KARL SAALBACH, Primary Examiner PAUL L. GENSLER, AssistantExaminer US. Cl. X.R. 333 24.2

